The conventional drag link suitcase has been widely used in for example a flight passenger suitcase and a heavy-goods carriage suitcase. With an extensible drag link, a suitcase can be transported in a labor-saving manner by being pulled and the space it occupies can be flexible subject to the need. However, the conventional drag link can be extensible only to its fullest length within the outer link without any capability of an intermediate positioning. Because of this there may be a problem in use if the drag link was partially closed within the outer link due to a mistake. Some improvement has been made by means of a conic retaining block located at the end of the inner link in order to retain it in position as soon as the drag link is pulled out. However, when the inner link is to be reinserted, the user has to use a large force to push down the puller to move the retaining block from its retaining position. This not only results in pain to the hand and inconvenience of operation, but also shortens the life of the drag link due to more wear and retaining strength damage. Therefore, it is obvious that the conventional drag link has such defects as a poor effective positioning and poor performance of use.